His departure was widely anticipated, but sometimes you have to follow the script, so now our attention turns to potential replacements such as Aisha Tyler and Neil Patrick Harris.

JOHN PAUL FILO/CBS; SONJA FLEMMING/CBS

David Letterman, Craig Ferguson

There was no surprise in the announcement that Craig Ferguson and CBS are parting ways, which is the prettiest of all ways to spin it. These things are important because good people did good work – that would be Ferguson – at a network good enough to give an opportunity to someone very much from the outside.

But it's not a surprise because, well, CBS already had a chance to give Ferguson a vote of confidence in the 12:30 a.m. slot and failed to act on it – which was, in itself, a way of acting on it.

And in the timeline of such things, once CBS gave David Letterman's chair to Stephen Colbert, that was the end. If Ferguson didn't get that job – it appears that he was never considered – then what was left? More of the same with no reasonable chance of promotion? Those are end times at virtually every job in America. It just so happens that Ferguson works in a higher profile job than most people.

Just from a business standpoint, CBS wasn't going to settle for the current arrangement, where Letterman's Worldwide Pants co-produces The Late Late Show. That was a perk given to Letterman and Worldwide Pants for, well, being Letterman and being employed on CBS. With that no longer a thing, neither was Ferguson.

So the proverbial writing on the wall was actually marked in neon. But even the least surprising news still carries with it some sting when it's bad news. Ferguson, roundly considered one of the nicest people in show business, quickly made a mark in the crowded late-night field by being different -- the rhythms of his show were vastly off-kilter compared to the playbook. His monologues were always his own style and the "feel" of The Late Late Show went, over time, from curious outsiders to really nice outsiders.

Ferguson imbued his show with warmth and storytelling and honest goofiness. He was not everybody's style, but that in itself became a calling card – we do things differently here. Ferguson is less showy and less "on" than his counterparts. Without trying to take any edge away from him, Ferguson was more "homespun" than traditional, higher-wattage chat shows. As late-night TV seeks to get younger, that was more of a liability after midnight. Without the also-older-skewing Letterman in front, that age and style difference would have become more pronounced.

And so now we have a change, the particulars of which are not as important as the actual replacement. That is, whether Ferguson left on his own or was nudged by the drumbeats to the most convenient exit is not important. He's out and CBS will need to replace him, which becomes topic No. 1 until there's an announcement.

I've been touting Aisha Tyler as a bold and smart pick for a while now. There's word that CBS is interested in Neil Patrick Harris, which would make sense if Colbert's Late Show stays in New York and even more sense since CBS entertainment president Nina Tassler loves Broadway. Harris has wide appeal and could easily do the job if he wanted, so he certainly can't be ruled out.

CBS already ruled out Chelsea Handler, which should send a message to all interested parties that CBS will call you first if it's interested – do not start your own campaign.

Of course, Harris is both white and male, so that's not much of a change (though he's openly gay, so that is – though Ellen DeGeneres already broke that barrier). A woman of color would certainly be a bolder choice and someone like Tyler, who is funny and a great conversationalist, seems almost too right to ignore.

But we have plenty of time for further guesswork. Right now we're just in follow-the-script mode. And the script, some time ago, called for Ferguson to leave gracefully. Both sides, in an era where this kind of thing isn't always standard operating procedure, handled that well.